IN THE NAME OF GOD THE COMPASSIONATE THE MERCIFUL

Histology Lecture 19 Digestive System Part 3

Digestive Glands Digestive glands are consist of: Salivary glands Pancreas Liver Gall bladder

Salivary Glands There are many minor salivary glands scattered throughout oral mucosa and three pairs of major salivary glands Three pairs of major salivary glands are: Submandibular glands Sublingual glands Parotid glands They have lobular organization composed of branched tubuloalveolar glands with connective tissue capsule and septa that organize the glands into lobes and lobules Each individual acinus is also invested by a thin layer of CT Saliva secretion is controlled by autonomic nerves Sympathetic stimulation = sparse thick saliva Parasympathetic stimulation = copious, watery saliva

Salivary Gland Cells Serous cells are actually seromucous cells that produce proteins and polysaccharides They are pyramidal and have basal spherical euchromatic nucleus Cytoplasm is basophilic due to presence of a developed RER, Golgi apparatus Apically located granules that are usually eosinophilic and rich in ptyalin (salivary amylase) Many basal mitochondria Intercellular canaliculi, plasmalemma processes Organized as acinus or demilune that secrete proteins, polysaccharides and ptyalin

Salivary Gland Cells Mucous cells are cuboidal or pyramidal Mucous cells have a heterochromatic basal flattened nucleus Apical cytoplasm is pale or blue/purple Their structure is acinar or tubular They have less RER, fewer mitochondria but greater GA Intercellular cacanaliculi and processes are much less than serous cells

Salivary Gland Cells Myoepithelial cells (Basket cells) have large processes which form desmosomal contact with acini and ducts cells, Their processes are rich in actin and myosin Basket cells have a common basal lamina with acinar cells They attach to basal lamina by hemidesmosome

Salivary Gland Ducts Intercalated duct are smallest branches lined by short, cuboidal or squamous cells and myoepithelial cells Striated duct have large diameter composed of cuboidal to low columnar cells which are eosinophilic, and secrete fluid and ions, basolateral membrane folded with Na – ATPase pump, elongated mitochondria Striated ducts join each other and forming intralobular ducts that are invested by more CT elements These ducts join each other and forming larger caliber ducts known as interlobular ducts (excretory ducts) Excretory duct have large diameter, large lumen, cuboidal or columnar cells, located outside of lobules

Parotid Gland The largest salivary gland but produce 30% of saliva Connective tissue capsule is well developed forms many septa divided the glands into lobes and lobules Branched acinar structure All serous cells, but actually they are seromucous Secrete amylase(Ptyalin) Lymphocytes and plasma cells are located in connective tissue elements produce IgA After 40 year of age adipose tissue invaded the gland

Submandibular Gland Extensive connective tissue capsule and abundant septa Branched tubuloacinar gland produce 60% of saliva Mucous and serous acini; mucous acini with limited number of serous demilunes About 80% of cells are serous (basophilic) Lysozyme, mucous and amylase Striated ducts are much longer than the other two glands

Sublingual Gland It is very small that produce 5% of total saliva Glands invested by scant CT capsule Branched tubuloacinar gland Mostly mucous cells in acini with some serous demilunes Produce mix saliva but mostly mucous saliva

Saliva Saliva includes water, enzymes, IgA, mucous, ions Primary saliva manufactured by acinar cells is isotonic with plasma Secondary saliva is altered by striated duct cells Moisten and lubricate food for swallowing Enzymes like amylase and lipase to begin digestion Saliva has protective effect on oral cavity tissues Participate in taste sensation IgA, lactoferrin, lysozyme have different role against antigens and microorganisms

Pancreas Pancreas is a mixed exocrine and endocrine gland Thin capsule with septa between lobules Exocrine part organized as a compound tubuloacinar glands similar to parotid gland Endocrine part are islets of Langerhans scattered among the excretory units Centroacinar cells occupy the lumen of the acini, these cells are beginning of the duct system Centroacinar cells are pale, low cuboidal with receptors for secretin and acetylcholin Intercalated ducts, Intralobular ducts, and interlobular ducts

Pancreas Serous cells are truncated pyramidal in shape basophilic,with a round nucleus that is located basally, RER, GA, and secretory granules Zymogen granules contain: trypsinogen, chymotrypsinogen, carboxypeptidase, ribonuclease, DNAase, lipase, elastase, amylase Secretion controlled by secretin and CCK from duodenum and vagus nerve Centroacinar cells and intercalated ducts manufacture a serous, bicarbonate-rich alkaline fluid Main pancreatic duct goes to duodenum

Liver Liver is the largest gland in the body, weighing about 1500 gr , it has endocrine and exocrine functions Dense irregular connective tissue capsule of liver is loosely attached to liver except at porta hepatis where blood and lymph vessels and bile ducts enter or exit the gland Receives portal blood (75%) from small intestine via portal vein and oxygenated blood from hepatic arteries (25%) CT elements are sparse, bulk of liver is composed of hepatocytes Liver has a lobular organization Classical lobule in which hepatocytes arranged as an hexagon Portal area (triad) is where three classical lobules are in contact with each other, more CT elements present, houses branches of hepatic artery, tributaries of portal vein, interlobular bile ducts, and lymph vessels

Liver Portal areas are isolated from liver parenchyma by modified hepatocytes which form the limiting plate Space of Möll separates the limiting plate from the CT elements of portal area Longitudinal axis of each classical lobule is occupied by central vein Hepatocytes radiate from central vein and separating from each other by vascular spaces known as hepatic sinusoids Limiting membrane pierced by inlet venules and inlet arterioles to join hepatic sinusoids Blood from periphery flows slowly through sinusoids into central vein

Liver Central vein terminates in sublobular vein, these veins also join each other forming collecting veins which in turn form hepatic veins In classical lobule concept blood flow from periphery to center of lobule Bile manufactured by hepatocytes flow in opposite direction in small intercellular spaces known as bile canaliculi Portal lobule is a triangular region that portal area is located in its center and central veins form apices of the triangle Hepatic acinus (acinus of Rappaport) is diamond-shaped, a distributing artery located in center of acinus, three regions of parenchyma surrounding the artery(zone I, II, III)

Liver The space between the anastomosing plates of hepatocytes are occupied by hepatic sinusoids Sinosuidal lining cells are fenestrated are not in contact with each other They prevent direct contact between blood and hepatocytes Resident macrophages known as Kupffer cells associated with lining cells The space that separates sinusoidal lining cells from hepatocytes is called perisinusoidal space (space of Disse) Microvilli of hepatocytes occupy much of the space Type III collagen that is present in space support lining cells(no basal lamina)

Liver Fat storing cells ( known as Ito cells or Stellate cells) may present in Disse space and store vitamin A Pit cells which are natural killer cells also may be seen in space of Disse Hepatocytes are polygonal 20-30 µm diameter, forming anastomosing plates of one to two thickness cells, eosinophilic with 1 or 2 spherical nuclei, In lateral domain bile canaliculi form between two cells, microvilli, Na-K ATPase and gap junctions are common characteristics of lateral domain Bile canaliculi between hepatocytes leading to hepatic ducts with simple cuboidal epithelium

Liver Sinunosoidal domains of cell membrane have many microvilli protrude to perisinusoidal space (of Disse), endocrine secretion of hepatocytes release here Hepatocytes are large cells which are contain RER, free ribosomes, several sets of Golgi apparatuses, SER, mitochondria, lipid droplets, glycogen Bile secreted from hepatocytes into bile canaliculi contains water, ions, bile salts and acids, phospholipids, cholesterol, & bilirubin

Liver Functions Glycogen storage Lipid metabolism Vitamin storage (A, D, B12 ) Bile production (Bile acids solubilize lipids and aid digestion) Detoxification of drugs and toxins in SER Synthesis of plasma proteins (albumin) Metabolism of lipid, carbohydrate, proteins Erythrocyte breakdown (Bilirubin formed in breakdown of RBC) Complex IgA with secretory component

Gall Bladder Mucosa is lined by simple columnar epithelium with two type of cells: more clear cells and infrequent brush cells Cells have microvilli, Na –K ATPase pump Epithelial layer is highly folded lamina propria is composed of loose CT, in the neck region lamina propria houses simple tubuloalveolar mucus glands Smooth muscle layer is composed of thin obliquely oriented fibers with perimuscular connective tissue Serosal and adventitial membrane Stores and concentrates 30-50 ml bile Cholecystokinin and acetylcholine stimulates contraction to force bile into small intestine CCK released from duodenum in response to lipids in duodenum

Department of Histology F.Rajaei